Preparation of xylylenediamine (XDA)

ABSTRACT

A process for preparing xylylenediamine, comprising the steps of ammoxidizing xylene to phthalonitrile and hydrogenating the phthalonitrile, which comprises contacting the vaporous product of the ammoxidation stage directly with a liquid organic solvent or with molten phthalonitrile (quench), 
     partly or fully removing components having a boiling point lower than phthalonitrile (low boilers) from the resulting quench solution or suspension or phthalonitrile melt and, after the low boiler removal and before the hydrogenation, removing products having a boiling point higher than phthalonitrile (high boilers).

RELATED APPLICATIONS

This application is a national stage application (under 35 U.S.C. 371)of PCT/EP2004/009885 filed Sep. 4, 2004 which claims benefit to Germanapplication 103 41 614.5 filed Sep. 10, 2003.

BACKGROUND

The present invention relates to a process for preparingxylylenediamine, comprising the steps of ammoxidizing xylene tophthalonitrile and hydrogenating the phthalonitrile.

Xylylenediamine (bis(aminomethyl)benzene) is a useful starting material,for example for the synthesis of polyamides, epoxy hardeners or as anintermediate for preparing isocyanates.

The term “xylylenediamine” (XDA) includes the three isomersortho-xylylenediamine, meta-xylylenediamine (MXDA) andpara-xylylenediamine.

The term “phthalonitrile” (PN) includes the three isomers,1,2-dicyanobenzene=o-phthalonitrile,1,3-dicyanobenzene=isophthalonitrile=IPN and1,4-dicyanobenzene=terephthalonitrile.

The two-stage synthesis of xylylenediamine by ammoxidizing xylene andsubsequently hydrogenating the resulting phthalonitrile is known.

EP-A2-1 113 001 (Mitsubishi Gas Chem. Comp.) describes a process forpreparing nitrile compounds by ammoxidizing corresponding carbocyclic orheterocyclic compounds, in which excess ammonia from the reactionproduct is recycled. Also described is the direct contacting of thevaporous product of the ammoxidation stage with a liquid organic solventwhich is in particular aliphatic or aromatic hydrocarbons (paragraphs[0045] and [0046]).

EP-A2-1 193 247 and EP-A1-1 279 661 (both Mitsubishi Gas Chem. Comp.)relate to a process for purifying isophthalonitrile (IPN) and to aprocess for preparing pure XDA respectively, in which the phthalonitrileis synthesized by ammoxidizing xylene, and the vaporous product of theammoxidation stage is contacted directly with a liquid organic solvent(quench). The organic solvent is selected from alkylbenzenes,heterocyclic compounds, aromatic nitriles and heterocyclic nitriles, andhas a boiling point which is below that of phthalonitrile (EP-A2-1 193247: column 4, paragraph [0018] and [0019]; EP-A1-1 279 661: columns4-5, paragraph [0023] and [0024]).

EP-A2-1 193 244 (Mitsubishi Gas Chem. Comp.) describes a process forpreparing XDA by hydrogenating phthalonitrile which is synthesized in apreceding stage by ammoxidizing xylene, in which the vaporous product ofthe ammoxidation stage is contacted directly with a liquid organicsolvent (quench) and the resulting quench solution or suspension is fedto the hydrogenation.

Preferred organic solvents are C₆-C₁₂ aromatic hydrocarbons such asxylene and pseudocumene (column 6, paragraph [0027] and [0028]).

DE-A-21 64 169 describes, on page 6, last paragraph, the hydrogenationof IPN to meta-XDA in the presence of an Ni and/or Co catalyst inammonia as a solvent.

Five parallel BASF patent applications each having the same applicationdate each relate to-processes for preparing XDA.

BRIEF SUMMARY

It is an object of the present invention to provide an improved,economically viable process for preparing highly pure xylylenediamine,in particular meta-xylylenediamine, with high yield and space-time yield(STY), which, at comparable throughputs to prior art processes (forexample EP-A2-1 193 244, EP-A1-1 279 661), enables smaller and/or fewerapparatus and machines as a consequence of reduced streams, inparticular solvent streams, including recycle streams.

We have found that this object is achieved by a process for preparingxylylenediamine, comprising the steps of ammoxidizing xylene tophthalonitrile and hydrogenating the phthalonitrile, which comprisescontacting the vaporous product of the ammoxidation stage directly witha liquid organic solvent or with molten phthalonitrile (quench), partlyor fully removing components having a boiling point lower thanphthalonitrile (low boilers) from the resulting quench solution orsuspension or phthalonitrile melt and, after the low boiler removal andbefore the hydrogenation, removing products having a boiling pointhigher than phthalonitrile (high boilers).

The process according to the invention preferably finds use forpreparing meta-xylylenediamine (MXDA) by hydrogenating isophthalonitrile(IPN) which is synthesized in a preceding stage by ammoxidizingmeta-xylene.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic illustration of a process for preparingxylylenediamine according to the present invention.

FIG. 2 shows a schematic illustration of a quench step with subsequentlow boiler removal and subsequent high boiler removal according to thepresent invention.

FIG. 3 shows a schematic illustration of a quench step with subsequentlow boiler removal and high boiler removal in a sidestream column, whilePN is obtained in the sidestream according to the present invention.

FIG. 4 shows a schematic illustration of a quench step with subsequentlow boiler removal and high boiler removal in a dividing wall column,while PN is obtained in the sidestream according to the presentinvention.

FIG. 5 shows a schematic illustration of a combination of the quenchstep with the low boiler removal in a column and subsequent high boilerremoval according to the present invention.

DETAILED DESCRIPTION OF THE DISCLOSURE

The process according to the invention can be performed as follows:

Ammoxidation stage:

The ammoxidation of xylene (o-, m- or p-xylene) to the correspondingphthalonitrile (ortho-xylene→o-phthalonitrile;meta-xylene→isophthalonitrile; para-xylene→terephthalonitrile) isgenerally carried out by processes known to those skilled in the art.

The ammoxidation of methyl aromatics is preferably carried out over amultioxide catalyst with ammonia and an oxygenous gas (oxygen or air orboth) in a fluidized bed reactor or a tube (bundle) reactor.

The reaction temperature is generally from 300 to 500° C., preferablyfrom 330 to 480° C.

The catalyst preferably contains V, Sb and/or Cr and is more preferablycomposed of [V, Sb and alkali metals] or [V, Cr, Mo and B], in each caseas an unsupported catalyst or on an inert support.

Preferred inert supports are SiO₂, Al₂O₃ or a mixture of both, orsteatite. Such a procedure is described, for example, in the BASF patentapplications EP-A-767 165 and EP-A-699 476, which are explicitlyincorporated herein by way of reference.

The BASF patent applications EP-A-222 249, DE-A-35 40 517 and DE-A-37 00710 also disclose suitable ammoxidation catalysts.

The ammoxidation may also be carried out in accordance with theprocesses described in the applications cited at the outset, EP-A2-1 113001, EP-A2-1 193 247, EP-A1-1 279 661 and EP-A2-1 193 244.

Quench:

The vapor produced in the ammoxidation, comprising the product of value,phthalonitrile, is contacted directly with a liquid organic solvent orwith liquid, i.e. molten, phthalonitrile (preferably that isomer whichcorresponds to the synthesized PN) (quench with a liquid organic solventor with molten phthalonitrile as a quench liquid, quenching agent).

The solvent used for the quench may already contain dissolved orsuspended phthalonitrile (preferably that isomer which corresponds tothe synthesized PN).

Preferred organic solvents for the quench are selected from the group ofaromatic hydrocarbons (in particular alkylaromatics, very particularlyalkylbenzenes), heterocyclic compounds, aromatic nitriles andheterocyclic nitriles and mixtures thereof.

Examples of such solvents which can be used are o-xylene, m-xylene,p-xylene, pseudocumene, mesitylene, ethylbenzene, methylpyridine,benzonitrile, m-tolunitrile, o-tolunitrile, p-tolunitrile,N-methyl-2-pyrrolidone (NMP), THF, methanol and 1,4-dioxane.

Particularly preferred solvents are tolunitrile, benzonitrile and NMPand mixtures thereof.

The organic solvent for the quench has a lower boiling point than thesynthesized PN (at the same pressure).

The sudden temperature reduction when contacting the vaporousphthalonitrile with the liquid solvent or with the molten phthalonitrile(quench) reduces the formation of undesired secondary and decompositionproducts which lead to a reduction in the quality of the phthalonitrileand finally of the XDA.

The vaporous phthalonitrile is absorbed by the quench directly into theliquid solvent or the molten phthalonitrile, resulting, in the case ofthe liquid organic solvent, in a solution and/or a suspension and, inthe case of the molten phthalonitrile, in a phthalonitrile meltcontaining the synthesized PN.

The organic solvent for the quench or the molten phthalonitrile for thequench may be used as fresh feed having a purity >99% by weight, inparticular >99.5% by weight.

Preference is given to using organic solvent recovered from the processor phthalonitrile prepared in the process as quench liquid. The purityhere of the quench liquid may also be ≦99% by weight, for example 90-98%by weight, especially when the impurities are substances which are notforeign to the process (i.e., inter alia, water, ammonia, benzonitrile,tolunitrile, xylene, o-, m- or p-methylbenzylamine, benzylamine,xylylenediamine).

The amount of the organic solvent used is generally such thatsolutions/suspensions are obtained which have a phthalonitrile contentof from 15 to 75% by weight, preferably from 25 to 60% by weight.

In the case of molten phthalonitrile as the quenching agent, the amountof molten phthalonitrile used depends substantially on the heat to beremoved in the quench.

The vaporous effluent of the ammoxidation, comprising the phthalonitrile(PN), is introduced into the liquid organic solvent or into the moltenphthalonitrile in a quench apparatus, for example preferably in afalling-film condenser (thin-film, trickle-film or falling-streamcondenser), in a jet apparatus or in a column. In this apparatus, thevaporous phthalonitrile may be conducted in cocurrent or incountercurrent with the liquid solvent or the molten phthalonitrile. Inthe case of cocurrent flow, the vaporous phthalonitrile is introducedinto the quench apparatus from above. It is advantageous to feed theliquid solvent or molten phthalonitrile tangentially at the top of thefalling-film condenser or to feed the liquid solvent or moltenphthalonitrile through one or more nozzles, in order to achieve completewetting of the interior wall of the quench apparatus.

To increase the surface area available for condensation, the quenchapparatus may be equipped with internals such as trays, structuredpackings or random packings.

The solvent or molten phthalonitrile for the quench may be used insingle pass or as circuit solution.

Advantageously, a portion of the quench solution or suspension orphthalonitrile melt is recycled (circulation).

A heat transferor installed in the circuit is used to cool the quenchsolution or suspension or phthalonitrile melt.

The temperature of the circulation medium and the circuit flow rate areset and adjusted with respect to each other in such a way that thedesired temperature in the quench exit is achieved. The smaller the flowrate of the circulation medium, the lower the temperature selected ofthe circulation medium and vice versa, although solubilities and meltingpoints, and also the hydraulic stress limits of the quench apparatus,have to be taken into account.

The flow rate of the freshly fed organic solvent is dependent upon thequench temperature. It is set in such a way that the desiredconcentration of the PN solution or suspension is obtained.

Since the solubility of PN in the organic solvent rises with increasingtemperature, a higher PN concentration in the solvent can be conveyedwith increasing quench exit temperature.

The circulation medium or the molten phthalonitrile is fed in togetherwith the fresh solvent or separately, at a suitable point in the quenchapparatus.

In general, heating of the organic solvent and/or of the circulationmedium used sets the temperature of liquid quench effluent to from 40 to180° C., preferably from 50 to 120° C., in particular from 80 to 120° C.

In the case of molten phthalonitrile as the quenching agent, heating ofthe molten phthalonitrile and/or of the circulation medium used sets thetemperature of the liquid quench effluent, to from 165 to 220° C.,preferably from 180 to 220° C., in particular from 190 to 210° C.

The absolute pressure in the course of quenching is generally from 0.5to 1.5 bar. Preference is given to conveying at slightly elevatedpressure.

Xylene, water, NH₃, CO₂, N₂, etc., which are generally present in thevaporous effluent of the ammoxidation are only partly or virtually notdissolved under the quench conditions in the quenching agent (organicsolvent or molten phthalonitrile), and are removed from the quenchapparatus in predominantly gaseous form.

Partial or complete removal of components having a boiling point lowerthan phthalonitrile (low boilers) (at the same pressure) from theresulting quench solution or suspension or phthalonitrile melt:

The lower the temperature in the quench step, the higher the proportionof water and secondary components which have a lower boiling point thanPN (at the same pressure) (for example benzonitrile, tolunitrile) in theliquid quench effluent.

In the process according to the invention, before the hydrogenation ofthe phthalonitrile, water and components having a boiling point lowerthan phthalonitrile (at the same pressure) (low boilers; for example,unconverted xylene, benzonitrile, tolunitrile, each as a heteroazeotropewith water, water, benzonitrile, tolunitrile; listing with increasingboiling point (at the same pressure); and in some cases alsobenzylamine, o-, m-, p-methylbenzylamine, xylylenediamines, these aminesstemming from recycled solvent from the hydrogenation stage) are partlyor fully removed from the resulting quench solution or suspension orphthalonitrile melt. This removal is preferably by distillation.

Preference is given to also partly or fully removing the organic solventused in the quench in this step as a low boiler.

This removal of the solvent and/or of the low boilers may be effected inone or more evaporator stages connected in series or in a distillationcolumn overhead, while phthalonitrile is removed via the bottom togetherwith products having a boiling point higher than phthalonitrile (highboilers) (at the same pressure).

Preference is given to using a distillation column which is equippedpreferably with the customary internals for increasing the separatingperformance, such as trays, structured or random packings, etc.

The configuration of the column (in particular number of separatingstages, feed point, reflux ratio, etc.) may, adapted to the particularcomposition of the solution or suspension, be carried out by thoseskilled in the art by methods familiar to them. Preference is given tooperating under reduced pressure, in order to limit the bottomtemperature.

In a particular embodiment of the process according to the invention,the quench of the vaporous product of the ammoxidation stage with aliquid organic solvent or with molten phthalonitrile is carried out in acolumn in such a way that reaction gases and low boilers, including anyorganic solvent used as a quenching agent, are removed partly or fullyoverhead and phthalonitrile, together with products having a boilingpoint higher than phthalonitrile (high boilers) is removed via thebottom. (See FIG. 5).

This particular procedure combines quench and low boiler removal in onestage (one step) and in a specific quench apparatus, a quench column.The circulation method already described above of a portion of thequench column effluent is again particularly advantageous, and it isrecycled as a quenching agent preferably into about the middle of thecolumn.

Subsequently, any low boilers still present may be removed fully fromthe resulting phthalonitrile by evaporation or rectification in asubsequent further step under reduced pressure. It is preferred that nofurther low boiler removal is carried out in this procedure, but ratherthat the resulting PN melts from the combined quench/low boiler removalstep are conveyed to the next step of high boiler removal.

The gaseous effluent from the ammoxidation is preferably introduced atthe column bottom of the quench column, and the fresh quenching agent(organic solvent) at the top (countercurrent), while the quench columneffluent consists of a mixture of solvent and PN or (depending on thetemperature selected) is virtually solvent free (cf. FIG. 5). Thecomposition of the quench column effluent is determined by the operatingconditions of the quench column (in particular temperature) and the flowrate of the solvent fed in at the top of the quench column.

In the case that PN melt is withdrawn at the bottom of the quenchcolumn, the organic solvent introduced at the top of the quench columnprevents the PN from being discharged overhead. This organic solvent isthus evaporated and removed virtually completely overhead. The flow rateto be introduced is to be adjusted accordingly.

With regard to the composition of the quench column effluent, thetransition from a solution of PN in the organic solvent, obtained at arelatively low bottom temperature of the quench column, and asubstantially solvent-free PN melt, obtained at a relatively high bottomtemperature of the quench column, is fluid.

The temperatures of the quench column effluent are generally as alreadydescribed for the quench step.

To obtain a PN melt in the bottom effluent of the quench column, theprocedure may be as follows:

The hot reaction gases from the ammoxidation are introduced in thebottom of a quench column, cf. FIG. 5. A portion of the bottom effluentis recycled and, after cooling to from approx. 165 to 180° C.,reintroduced at about the middle of the column. It has to be ensuredthat the temperature does not go below the melting temperature. The flowrate of the circuit melt has to be adjusted in such a way that thethermal output required can be removed. The column is equipped withinternals, for example trays or structured packings, to increase theseparating performance. At the top of the column, an organic solventhaving a boiling point smaller than that of PN is introduced. Thisresults in vaporous PN condensing in the upper section of the column andat the same time in the solvent evaporating. This ensures that virtuallyno PN is discharged via the top of the quench column. The bottomeffluent consists of PN with small fractions of the solvent, and alsosecondary components from the ammoxidation. The low-boiling secondarycomponents may be removed in a subsequent distillation stage. However,preference is given to conveying the melt to the high boiler removalwithout further low boiler removal.

Removal of products having a boiling point higher than phthalonitrile(high boilers) (at the same pressure) after the low boiler removal andbefore the hydrogenation:

The high boilers are preferably removed by distillation.

The high boilers may be removed in one or more successive evaporativestages or in one distillation column, in which case the high boilers aredischarged via the bottom, while phthalonitrile is removed overhead.

Preference is given to using a distillation column for the high boilerremoval.

The column is preferably equipped with the customary internals forincreasing the separating performance, such as trays, structured orrandom packings, etc.

The configuration of the column (in particular number of separatingstages, feed point, reflux ratio, etc.), adapted to the particularcomposition of the mixture to be separated, may be carried out by thoseskilled in the art by methods familiar to them.

Preference is given to operating under reduced pressure, in order tolimit the bottom temperature.

Combination of the low boiler and high boiler removal in a sidestreamcolumn, in particular dividing wall column with sidestream:

The removal of high boilers via the bottom and the removal of lowboilers overhead from the resulting quench solution or suspension orphthalonitrile melt is more preferably effected in a single column whichis configured as a sidestream column.

The phthalonitrile is withdrawn in liquid form from a sidestream in therectifying section or in vapor form from a sidestream in the strippingsection of the column. (See FIG. 3).

The configuration of the column (in particular number of separatingstages, feed point, reflux ratio, location of the sidestream, etc.) may,adapted to the particular composition of the solution, be carried out bythose skilled in the art by methods familiar to them.

Preference is given to operating under reduced pressure (for examplefrom 30 to 250 mbar (abs.), in particular from 50 to 100 mbar (abs.)),in order to limit the bottom temperature.

In a further particular process embodiment, the high boilers are removedvia the bottom and the low boilers are removed overhead from theresulting quench solution or suspension or phthalonitrile melt in asingle column which is configured as a dividing wall column with asidestream.

The phthalonitrile is withdrawn in liquid form from a sidestream in theregion of the dividing wall (see FIG. 4).

Suitable dividing wall columns are known to those skilled in the art,for example, from Hydrocarbon Processing, March 2002, page 50 B—50 D;EP-A-1 040 857, DE-A1-101 00 552, WO-A-02/40434, U.S. Pat. No.4,230,533, EP-A1-638 778, EP-A1-1 181 964, WO-A-02/45811, EP-A1-1 205460, DE-A1-198 13 720, EP-A1-1 084 741.

Hydrogenation:

The crude phthalonitrile obtained as described above after the lowboiler and high boiler removal is subsequently fed to the hydrogenation.

For the hydrogenation of the phthalonitrile to the correspondingxylylenediamine (o-, m- or p-xylylenediamine), particular preference isgiven to adding ammonia, preferably in liquid form, to the PN.

For the hydrogenation of the phthalonitrile, it is also possible to addan organic solvent. When the hydrogenation is carried out in thepresence of ammonia and an organic solvent, preference is given to firstpreparing the solution or suspension in the solvent.

Preferred solvents here are NMP, xylene, benzylamine, o-, m- orp-methylbenzylamine, xylylenediamine and mixtures thereof.

A preferred embodiment consists in the sole use of liquid ammonia as thesolvent.

The weight ratio in the fresh feed of dinitrile to ammonia used isgenerally from 1:0.15 to 1:15, preferably from 1:0.5 to 1:10, morepreferably from 1:1 to 1:5.

For the hydrogenation, the catalysts and reactors (for example fixed bedor suspension method), and also processes (continuous, semicontinuous,batchwise), which are known to those skilled in the art for thisreaction may be employed.

In the fixed bed catalyst method, both the liquid phase and the tricklemethod are possible. Preference is given to a trickle method.

In this regard, reference is made, for example, to the processesdescribed in the applications GB-A-852,972 (equivalent: DE-A-11 19 285)(BASF AG) and DE-A-12 59 899 (BASF AG) and to the U.S. Pat. No.3,069,469 (California Research Corp.).

The hydrogenation reactor may be operated in straight pass.Alternatively, a circulation method is also possible, in which a portionof the reactor effluent is recycled to the reactor inlet, preferablywithout preceding workup of the circulation stream. This allows optimumdilution of the reaction solution to be achieved, which has a favorableeffect on the selectivity. In particular, the circulation stream may becooled in a simple and inexpensive manner by means of an external heattransferor, and the heat of reaction thus removed. The reactor can alsobe operated adiabatically, in which case the temperature rise of thereaction solution may be limited by the cooled circulation stream. Sincethe reactor itself then does not have to be cooled, a simple andinexpensive design is possible. An alternative is a cooled tube bundlereactor.

Preference is given to catalysts which contain cobalt and/or nickeland/or iron, as an unsupported catalyst or on an inert support.

The reaction temperatures are generally from 40 to 150° C., preferablyfrom 40 to 120° C.

The pressure is generally from 40 to 300 bar, preferably from 100 to 200bar.

Isolation of the XDA:

After the hydrogenation, any solvent used and any ammonia used aredistilled off.

Preference is given to purifying the xylylenediamine by distilling offrelatively low-boiling by-products (at the same pressure) overhead andremoving relatively high-boiling impurities via the bottom bydistillation.

Particular preference is given to the method in which, after thehydrogenation, any solvent used, any ammonia and also any relativelylow-boiling by-products are distilled off overhead and, afterwards,relatively high-boiling impurities are removed from the xylylene bydistillation via the bottom.

In a particular embodiment, the removal of relatively low-boiling andrelatively high-boiling by-products may also be effected in a sidestreamor dividing wall column, in which case pure xylylenediamine may beobtained via a liquid or gaseous sidestream.

Depending on the desired purity, the product (XDA) is additionallyextracted with an organic solvent, preferably an aliphatic hydrocarbon,in particular a cycloaliphatic hydrocarbon, very particularlycyclohexane or methylcyclohexane.

This purification by extraction may be effected, for example, accordingto DE-A-1 074 592.

A schematic overview of a preferred embodiment of the process accordingto the invention is given by FIG. 1 in the appendix.

The optional process features, ‘organic solvent in the hydrogenation’and ‘extractive XDA purification’ are indicated by dashed lines.

FIG. 2 shows a scheme of the quench step with subsequent low boilerremoval (including quench solvent) and subsequent high boiler removal.

FIG. 3 shows a scheme of the quench step with subsequent low boilerremoval (including quench solvent) and high boiler removal in asidestream column, while PN is obtained in the sidestream.

FIG. 4 shows a scheme of the quench step with subsequent low boilerremoval (including quench solvent) and high boiler removal in a dividingwall column, while PN is obtained in the sidestream.

FIG. 5 shows a scheme of the combination of the quench step with the lowboiler removal (including quench solvent) in a column and subsequenthigh boiler removal.

EXAMPLES Example 1

Ammoxidation of m-xylene, subsequent quenching of the reaction gaseswith tolunitrile as a solvent, low boiler removal, high boiler removaland hydrogenation of the IPN formed in the ammoxidation stage (cf.process scheme in FIG. 1)

A catalyst having the composition V₄Sb₃W_(0.4)Cs_(0.2) on steatite wasinstalled into a tubular reactor as a fixed bed. The apparatus washeated externally to 400° C. Evaporated m-xylene, gaseous ammonia, airand nitrogen were introduced to the reactor (NH₃/m-xylene=8 mol/1 mol;O₂/m-xylene=4 mol /1 mol). The furthest upstream part of the reactor wasfilled with an inert bed, so that the starting materials reached thereaction zone premixed and preheated to 400° C. In the reactor there wasa slightly elevated pressure of 0.2 bar. The hotspot temperature reached450° C. After conversion (C) of m-xylene of 79%, a selectivity (S) forIPN of 68% was achieved.

The gas mixture leaving the reactor is quenched in a column withtolunitrile. A solution of IPN in tolunitrile is discharged from thequench column at 120° C. and contains 1% by weight of m-xylene, 0.3% byweight of water, 0.1% by weight of benzonitrile, 80% by weight oftolunitrile and 18.7% by weight of IPN. Unconverted reaction gases andinert gases, and also unconverted m-xylene and a little tolunitrile, arewithdrawn in gaseous form via the top of the quench column. This gas maybe worked up, in order to recycle the materials of value (in particularNH₃, m-xylene, and tolunitrile) into the reaction stage or into thequench circuit. Inerts and secondary components (H₂O, benzonitrile, N₂,CO₂, etc.) are discharged from the workup stage.

The solution of IPN in tolunitrile obtained after the quench is fed at100 mbar (abs.) to one of the middle stages of a distillation column.Xylene, tolunitrile, benzonitrile and water are removed overhead at 57°C. IPN having less than 0.1% by weight of tolunitrile is withdrawn viathe bottom together with the high-boiling secondary components present.The bottom temperature is 195° C. The top withdrawal stream may beworked up and recycled to the ammoxidation or to the quench circuit.

27% by weight of IPN were mixed with 73% by weight of NMP andhydrogenated in a continuously operated 70 ml tubular reactor over anunsupported cobalt catalyst at 80° C. and 190 bar. Every hour, 70 g ofIPN solution and 90 g of ammonia were passed over the catalyst. Theyield of MXDA was 96% based on IPN used.

In a subsequent batch distillation, first ammonia which was stilldissolved and then NMP and low-boiling secondary components wereremoved. After removal of the high-boiling impurities, MXDA was obtainedin a purity of more than 99.9% by weight.

Example 2 Alternative Hydrogenation Conditions

A mixture consisting of 27% by weight of IPN and 73% by weight of NMP,which was mixed together from the pure components, was hydrogenated in acontinuous 70 ml tubular reactor over an unsupported cobalt catalyst at80° C. and 190 bar. Every hour, 70 g of IPN solution and 54 g of ammoniawere passed over the catalyst. The same volume flow rate is recycled asa solvent. The yield of MXDA was 95.5% based on IPN used.

Example 3 Alternative Hydrogenation Conditions

A mixture consisting of 15% by weight of IPN and 85% by weight of MXDA,which was mixed together from the pure components, was hydrogenated in acontinuous 70 ml tubular reactor over an unsupported cobalt catalyst at60° C. and 190 bar. Every hour, 117 g of IPN solution and 150 g ofammonia were passed over the catalyst. A quarter of the volume flow rateis recycled as a solvent. The yield of MXDA was 92% based on IPN used.

In subsequent distillation steps, first ammonia and then low-boilingsecondary components were removed. After removing the high-boilingimpurities via the bottom, MXDA was obtained as a top product of adistillation column in a purity of more than 99.9% by weight.

Example 4(Alternative Hydrogenation Conditions)

30 g of IPN and 5 g of Raney nickel were initially charged in a stirredautoclave. After 66 g of ammonia had been added, 50 bar of hydrogen wereinjected and the autoclave was heated to 100° C. Injection of furtherhydrogen maintained an overall pressure of 100 bar for 5 hours. Theconversion of IPN was quantitative, and a yield of 94% based on IPN usedwas obtained.

(The data of the quench step reported above are the results of athermodynamic simulation. In this simulation, the quench was consideredto be an apparatus in which there is thermodynamic equilibrium betweengas and liquid phase. In addition to the pure material data of thecomponents involved, real binary data were used in the calculation. Suchcalculations can be carried out with commercial calculation programs,here: ASPEN PLUS, which are familiar to those skilled in the art.)

Example 5

Investigations of solubility of IPN in different solvents

The solubility of IPN in NMP is approx. 26% by weight at 60° C. andapprox. 41% by weight at 90° C.

At 90° C., pseudocumene attains a solubility of only 20% by weight andmesitylene of only 12% by weight.

At 60° C., the solubility of IPN in mesitylene or pseudocumene is ineach case below 10% by weight.

1. A process for preparing ortho-, meta- or para-xylylenediamine,comprising the steps of ammoxidizing ortho-, meta- or para-xylene tophthalonitrile, iso- or terephthalonitrile and hydrogenating thephthalonitrile, which comprises contacting the vaporous product of theammoxidation stage directly with a liquid organic solvent or with moltenphthalonitrile (quench), partly or fully removing components having aboiling point lower than phthalonitrile (low boilers) from the resultingquench solution or suspension or phthalonitrile melt and, after the lowboiler removal or in combination with the low boiler removal and beforethe hydrogenation, removing products having a boiling point higher thanphthalonitrile (high boilers).
 2. The process according to claim 1 forpreparing meta-xylylenediamine, comprising the steps of ammoxidizingmeta-xylene to isophthalonitrile and hydrogenating theisophthalonitrile.
 3. The process according to claim 1, wherein theliquid organic solvent used for the quench is an aromatic hydrocarbon, aheterocyclic compound, an aromatic nitrile and/or a heterocyclicnitrile.
 4. The process according to claim 1, wherein the liquid organicsolvent used for the quench is tolunitrile, benzonitrile and/orN-methyl-2-pyrrolidone (NMP).
 5. The process according to claim 1,wherein, in the quench with a liquid organic solvent, the temperature ofthe quench effluent is from 40 to 180° C., and, in the quench withmolten phthalonitrile, the temperature of the quench effluent is from165 to 220° C.
 6. The process according to claim 1, wherein the lowboilers are partly or fully removed from the resulting quench solutionor suspension or phthalonitrile melt by distillation overhead, whilephthalonitrile is removed via the bottom together with products having aboiling point higher than phthalonitrile (high boilers).
 7. The processaccording to claim 1, wherein the high boilers are removed via thebottom by distillation, while phthalonitrile is removed overhead.
 8. Theprocess according claim 1, wherein the quench of the vaporous product ofthe ammoxidation stage is carried out in a column in such a way thatreaction gases and low boilers are partly or fully removed overhead andphthalonitrile together with high boilers are removed via the bottom. 9.The process according to claim 1, wherein the resulting quench solutionor suspension or phthalonitrile melt is separated into low boilers, highboilers and phthalonitrile in a sidestream column in such a way thathigh boilers are removed via the bottom, low boilers via the top andphthalonitrile via a sidestream.
 10. The process according to claim 1,wherein the resulting quench solution or suspension or phthalonitrilemelt is separated into low boilers, high boilers and phthalonitrile in adividing wall column in such a way that high boilers are removed via thebottom, low boilers via the top and phthalonitrile via a sidestream inthe dividing wall region of the column.
 11. The process according toclaim 1, wherein the ammoxidation is carried out at temperatures of from300 to 500° C. over a catalyst containing V, Sb and/or Cr, as anunsupported catalyst or on an inert support.
 12. The process accordingclaim 1, wherein the hydrogenation is carried out in the presence ofammonia.
 13. The process according to claim 1, wherein the hydrogenationis carried out in the presence or absence of an organic solvent.
 14. Theprocess according to claim 1, wherein the hydrogenation is carried outat temperatures of from 40 to 150° C. over a catalyst containing Ni, Coand/or Fe, as an unsupported catalyst or on an inert support.
 15. Theprocess according to claim 1, wherein, after the hydrogenation, thexylylenediamine is purified by distilling off any solvent used andammonia, and also any relatively low-boiling by-products, overhead anddistillatively removing relatively high-boiling impurities via thebottom.
 16. The process according to claim 1, wherein, after thehydrogenation, any solvent used and ammonia, and also any relativelylow-boiling by-products, are distilled off overhead and, afterwards, anyrelatively high-boiling impurities are removed from the xylylenediamineby distillation via the bottom.
 17. The process according to claim 16,wherein the xylylenediamine, after the distillation, is extracted forfurther purification with an organic solvent.
 18. The process accordingclaim 17, wherein cyclohexane or methylcyclohexane are used for theextraction.
 19. The process according to claim 15, wherein thexylylenediamine, after the distillation, is extracted for furtherpurification with an organic solvent.
 20. The process according claim19, wherein cyclohexane or methylcyclohexane are used for theextraction.